Imidazolines are a family of compounds based on a five-membered ring structure containing two nitrogen atoms and a double bond. The ring is numbered in such fashion that the nitrogens carry the lowest combination of numbers: ##STR1##
Commercially, imidazolines are made from the reaction of fatty acid, fatty alkyl (e.g. methyl) esters, or fatty triglycerides with a polyamine such as diethylenetriamine (DETA), aminoethylethanolamine (AEEA), ethylenediamine (EDA), or triethylenetetramine (TETA). The intermediate amidoamine is dehydrated to yield the cyclic imidazoline product.
While the manufacture of imidazolines on a commercial scale is relatively easy, the product is not easy to store or use without hydrolysis. Numerous authors have commented on the instability of the imidazoline molecule. Linfield, JAOCS, 61, No. 2 (1984), p 439, states that the imidazolines are unstable and in the presence of water revert back to the amidoamine starting material by standing overnight at room temperature. Wechsler, et al., U.S. Pats. Nos. 4,269,730 and 4,189,593, caution that during the reduced pressure dehydration to make the imidazoline, care must be taken to avoid any contact between the reactant and air which would cause rapid and severe darkening of the product. Butler, et al., J. Chem. Res., (5), 84 (1981) report decomposition of the imidazoline ring under atmospheric conditions in 2-9 days provided the compound contains a cis-olefin system. Bristline, et al., JAOCS, 60, No. 4 (1983), p 823, showed that the imidazoline ring content in a system decreased from 38% to 6% imidazoline in 72 hours with the addition of 2% H.sub.2 O (half-life of 24 hours). Even in a sealed container, these authors reported 5-8% loss in ring content over 18 months. Their conclusion was that, "When used as intermediates, imidazolines should be reacted promptly and prolonged storage should be avoided". Bristline, et al., JAOCS, 60, (1983), p 1676, showed that, "The imidazoline is hydrolyzed quantitatively to the diamide in the presence of water in ca. four days at room temperature."
This well-documented hydrolytic instability has inhibited the commercialization of imidazolines for aqueous applications. When imidazolines are protonated or quaternized, however, their hydrolytic stability is dramatically increased as is their water compatibility. Commercial producers, then, often manufacture the protonated or quaternized derivatives of imidazolines. Imidazoline-derived amphoterics, such as the chloroacetate derivative, are known to be excellent foamers and good cleaners, yet are substances of low toxicity possessing properties of low-irritancy to both skin and eye. Hunting, "Amphoteric Surfactants", Cosmetics & Toiletries, 95, November 1980, p 95, and references cited therein, reports that these amphoterics also are bacteriostatic.